As a system for restraining a vehicle occupant during a collision, an occupant restraining device that prevents a so-called submarine phenomenon is known. Specifically, a submarine phenomenon occurs when an occupant wearing a seatbelt slips through a space below a lap belt during a frontal collision. Japanese Unexamined Patent Application Publication No. 10-217818 discloses an occupant restraining device having an inflatable bag disposed between a seat cushion and a seat pan. When a vehicle is involved in a collision, the bag inflates and pushes the front portion of the seat cushion upward.
FIG. 7 is a longitudinal sectional view of the occupant restraining device of Japanese Unexamined Patent Application Publication No. 10-217818 as viewed in a front-back direction of a seat. At the front portion of the seat, an airbag 44 is disposed between a cushion frame (seat pan) 40 and a seat pad 42. The airbag 44 extends in a left-right width direction of the seat and can be inflated by an inflator 46. The upper surface of the seat pad 42 is covered with a trim cover 48 on which an occupant can be seated.
When the inflator 46 is actuated in response to a collision of the vehicle, the airbag 44 is inflated, causing the front portion of the seat pad 42 to be pushed upward or to be thrust upward from below. This increases the density, thereby preventing (including suppressing) forward movement of the occupant's body.
Such an airbag 44 is typically formed by stacking two sheets of woven fabric one on top of the other and sewing the two together along the edges thereof.